Hazardous fluids are routinely conveyed within enclosed pipes or conduits. Recognizing that such pipes and conduits can leak due to any of numerous causes, such as manufacturing defects, excessive pressure, corrosion, joint defects, and other defects created by thermal stresses, double-containment piping systems have been developed in which an inner pipe system (also referred to as the "carrier" or "primary" pipe system) is located within an outer pipe system (also referred to as the "containment" or "secondary" pipe system). An axially-extending space, typically in the form of an annulus, is defined between the inner and outer pipe systems for receiving and containing any fluids that might leak from the inner or carrier piping components. The inner pipes are typically supported by either resting on a lower, inside wall of the outer pipes, or alternatively, by intermediate supports mounted between the inner pipes and the outer pipes for supporting the inner pipes in spaced relation to the outer pipes and thereby forming an annulus between the inner and outer pipes.
Intermediate supports are typically designed to permit axial movement, but tend to constrain lateral movement of the inner pipes relative to the outer pipes in order to maintain the inner and outer pipes in an approximately coaxial relationship (these types of supports have been referred to as "centering supports"). However, other types of intermediate supports are designed to permit both axial and lateral movement of the inner pipes relative to the outer pipes in order to accommodate differential thermal expansion. Exemplary prior art intermediate supports for double-containment pipe systems are illustrated in U.S. Pat. Nos. 5,141,184; 5,018,260; 4,751,945; 3,863,679; and U.S. Pat. No. 3,417,785. Double-containment pipe fittings, such as elbow fittings, tee fittings, lateral and/or reducing fittings, tee-wye branch fittings, etc., may be also provided with supports for centralizing, and often anchoring the inner pipes connected to the fittings. Exemplary prior art fitting and anchor support assemblies of this type are shown in U.S. Pat. Nos. 4,886,305; 5,186,502; and 5,398,973.
For double-containment pipe systems subject to relatively moderate differential thermal expansion, the problem has been addressed in the prior art by employing the above-described fitting and anchor support assemblies with intermediate centering supports spaced relative to each other between the anchor supports. In these types of systems, the outer or containment pipes are typically anchored within the soil in underground installations, and otherwise are anchored with suitable supports in aboveground installations. Thus, the above-described fitting and anchor support assemblies restrain and substantially prevent any axial expansion of the carrier pipes, and the intermediate supports are designed and positioned to prevent buckling of the carrier pipes between the fitting and anchor support assemblies. Since any thermal expansion is restrained, the inner pipes or carrier components are subjected to compressive stress. If the magnitude of this stress, and the resulting strain within the system is held within specified limits, then this type of arrangement can effectively control and compensate for any thermal expansion of the carrier pipe system. This type of arrangement is particularly effective for controlling thermal expansion in double-containment pipe systems employing materials that do not perform well in bending, such as certain types of piping made of reinforced thermosetting resin that employ adhesively-bonded joints, and piping made of certain types of thermoplastics that employ solvent-cemented joints. In these types of systems, the magnitude of bending that may occur in a flexible system can cause a failure, typically at a joint, and therefore a restrained system is often a better choice.
One of the drawbacks of the prior art fitting and anchor support assemblies is that they typically must be joined to the respective carrier and containment pipes and other components by adhesive bonding (in RTRP or thermoplastic systems), solvent cementing (in thermoplastic systems), hot gas welding (in thermoplastic systems), or welding (in metallic systems). The welding/bonding processes, which are often difficult to perform due to the complexities of the assemblies, can require substantial construction and assembly time and thus involve substantial costs. The welding/bonding processes also typically require that the supports be made of the same material as either the inner and/or the outer pipes so that they can be properly welded or bonded to the respective pipes. Accordingly, any flexibility in selecting the materials of the anchor supports is typically limited by the materials of the inner and/or outer pipes.
In addition, the configurations of the prior art fitting and anchor support assemblies typically require a different geometry depending upon the type of fitting to be joined (e.g., 90.degree. elbow, 45.degree. elbow, tee, lateral, etc.). Furthermore, the prior art designs typically require a different internal anchor design for each given pipe size, thereby increasing the number of parts required on hand and the overall costs of the double-containment pipe systems.
Accordingly, it is an object of the present invention to provide anchor supports for double-containment pipe assemblies which overcome one or more of the drawbacks and disadvantages of the prior art.